Embodiments of the present disclosure generally relate to a memory system, and more particularly to a technology for reducing current consumption needed to perform a refresh operation in a Dual In-line Memory Module.
A memory cell of a dynamic semiconductor memory such as a dynamic random access memory (hereinafter referred to as “DRAM”) stores data in a capacitive element. Due to leakage of charges from the capacitive element, the memory cell must be periodically refreshed. A refresh process may include the process of reading data from a certain memory cell and rewriting the read data to the same memory cell.
There are various types of refresh methods that have been used in the dynamic semiconductor memory. Auto refresh is a refresh method that performs refresh operations in response to a periodic refresh command provided from a controller. The semiconductor memory may perform auto refresh operations according to a refresh timer located outside the semiconductor memory.
Self refresh is a refresh method that uses an internal refresh timer located inside the memory chip. According to an example, the semiconductor memory may request a refresh start command from the controller.
Typically, it is impossible for a memory cell to be accessed for the normal read and write operations while the memory cell is being refreshed. A refresh operation lasts for a time referred to as the refresh cycle time (“tRFC”), and then an active cycle may start an operation.
Memory cells may have different data retention times. Therefore, if the same refresh operation is performed on all the memory cells, unnecessary current consumption may occur.
Lower power consumption is the dominant requirement in designing a mobile product, and thus it is very important to reduce current consumption caused by the refresh operation.